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Purpose: We developed an infrared flat-bed scanner with a transparency unit (IR 4000, iMeasure, Inc.) in order to increase the sensitivity of measuring density of Gafchromic EBT film (International Specialty Products). Then, the performance of IR 4000 was investigated, comparing with a general-purpose flat-bed scanner. Methods and Materials: Gafchromic EBT film (EBT) has the absorption spectrum with a maximum absorption band centered at 636 nm. Consequently the response of EBT will be enhanced by measurement with red light. Then, the transparency unit of IR 4000 for EBT has light emitting diode (LED) with a peak wavelength of 630 nm, and was produced by replacing LEDs of white light in the transparency unit for the flat-bed scanner (ES 2200, Seiko Epson Corp). Samples of EBT were covered with solid water RMI-457 phantoms and were exposed to the following doses: 0.3 – 10.0 Gy with the 6 MV photon beam from a Siemens MEVATRON77 DX67 accelerator. The irradiated samples were scanned by IR 4000 with 48 bit color mode and 1200 dpi and the scan data of red channel was converted into optical density. And also, the samples to which the yellow filter (International Specialty Products) was added were scanned by ES 2200. Furthermore the optical density by the two scanners was divided by the absorbed dose and the value was estimated as sensitivity. Result and Discussion: EBT using IR 4000 was about 1.60 times more sensitive on the average than using ES 2200 with the yellow filter in the dose range from 0.3 Gy to 10.0 Gy. By using IR 4000, the increase of sensitivity for EBT is easily achieved without using the filter which has the problem of dust, scratch or oxidation. Conclusion: The high capability of all Gafchromic films is utilizable by employing IR 4000 which has the easily exchangeable transparency unit. |
